Power amplifiers for cellular handsets are optimized for efficiency at, or close to, maximum output power. However, in the field, they may only be called upon to operate near maximum output power for a very small percentage of the time. The rest of the time, they may be operating at back-off output power levels, where their DC to radio-frequency (RF) conversion efficiency is very much reduced. This loss in efficiency under practical conditions results in increased thermal dissipation in the handset and reduced talk time.